1. Field of the Art
The present invention relates in general to a rotary compressor having a rotor rotated in a housing an a plurality of compression chambers whose volume is changed as the rotor is rotated to compress a gas sucked through a suction port and deliver the compressed gas through a discharge port. More particularly, the invention is concerned with such a rotary compressor of variable delivery type which is capable of reducing its displacement or delivery from the nominal maximum by means of disabling the compression chambers for given periods of time.
2. Related Art Statement
Rotary compressors of the type indicated above are used, for example, as a refrigerant compressor for an air-conditioning system in an automotive vehicle. The compressor is required to provide a large delivery while the air-conditioning system is operated in a mode to lower the room temperature of the vehicle. After the room temperature has been lowered to a comfortable level, the air-conditioning system is switched from the temperature lowering mode to a mode to maintain the room temperature. In the latter mode for maintaining the temperature at a constant level, the compressor is not required to operate at its nominal maximum or full-capacity rating, and should preferably be operated at a reduced capacity rating so as to provide a reduced delivery.
To this end, a rotary compressor is proposed according to U.S. Pat. No. 4,060,343, which uses a rotary plate having a by-pass passage for communication between a compression chamber which is compressing a gas, and a compression chamber which is sucking the gas. In this compressor, upon a decrease in the cooling load applied to the compressor, the rotary plate is rotated as by a hydraulic actuator to shift the position of the discharge-side edge of the opening of the by-pass passage toward the discharge port in the rotating direction of the rotor, in order to retard the timing of starting the compression of the gas in the compression chamber and thereby reduce the delivery of the compressor.
The above proposed arrangement is advantageous in that the compressor is automatically switched to its reduced-delivery mode when the cooling load is reduced below a certain level. However, the proposed compressor suffers some inconveniences that should be solved.
More specifically, the compressor using such a rotary plate for retarding the compression timing of the compression chamber requires the rotary plate to be rotatable by a relatively large angle to obtain a sufficient shifting distance of the discharge-side end position of the by-pass passage for achieving a sufficient degree of reduction in the delivery of the compressed gas. For this reason, the compressor inevitably requires a complicated and large-sized device for actuating the rotary plate.
In view of the above incoveniences, the assigneee of the present application developed a rotary compressor as disclosed in Laid-open Publication No. 59-183098 of Japanese Patent Application No. 58-58846 (filed in 1983), which uses a closure member which is movable between a first position in which the closure member fills a portion of a suction port on the side nearer to a discharge port in the rotating direction of the rotor (hereinafter simple called "discharge-side" portion of the suction port), and a second position in which the discharge-side portion of the suction port is not occupied by the closure member. When the cooling load is reduced, the closure member is moved to its second position to shift the discharge-side edge or end of the suction port toward the discharge port, and thereby retard the compression start timing of the compression chamber. Thus, the delivery of the compressor is reduced.
In the rotary compressor disclosed in the above-identified Japanese Patent Application, a comparatively small movement of the closure member permits a comparatively large shift of the discharge-side end or extremity of the suction port. Hence, the arrangement in question has eliminated the previously indicated problem associated with the rotary plate. That is, the actuator for the rotary plate tends to be complicated and large-sized. Nevertheless, the arrangement using the closure member has the following problem.
In the case that the start of compression of the gas in the compression chamber is retarded by changing the position of the discharge-side extremity of the suction port, the gas once sucked into the leading compression chamber is difficult to be discharged into a suction chamber or difficult to flow into the flowing compression chamber which is sucking the gas, while the compresser speed and the inertia of the gas are relatively high. In such conditions, it is difficult to expect a sufficient degree of reduction in the compressor delivery.
Another form of variable-delivery rotary compressor is proposed according to Laid-open Publication No. 59-99089 of Japanese Patent Application No. 57-209016 (filed in 1982), wherein a spool valve is provided in a suction passage communicating with a compression chamber in a sucking process (sucking compression chamber). In this compressor, the effective area of suction of the suction passage is reduced by the spool valve to reduce the compressor delivery when the cooling load is lowered.
Although the above arrangement permits sufficient reduction of the compressor delivery during a high-speed operation of the compressor, the reduction of the suction area of the suction passage may not result in sufficient delivery reduction while the compressor speed is low, because a large amount of gas may be sucked into the compression chamber through the suction passage even when the suction area is reduced while the compressor speed is low. Further, the instant proposed arrangement using the spool valve is less effective in preventing the compression of a fluid (e.g., refrigerant) in the liquid state and an abrupt increase in the engine load of the vehicle upon starting the compressor, as compared with the previously indicated arrangement wherein the position of the discharge-side end of the suction port is shifted.
In conclusion, none of the aforementioned rotary compressors known in the art is capable of effecting a sufficient degree of reduction in its delivery over the entire range of operating speed.